1. Field of the Invention
This invention relates to a pallet type multi-station conveyor wherein the pallets are nonsycronously conveyed from station to station by a continuously driven endless chain and particularly a device for adjusting the adhesive friction between a pallet and a endless chain in the pallet conveyor.
2. Prior Art
This type of conventional multi station conveyor comprises elongated frames which constitute a top linear path of the pallets with a continuously driven endless chain and a bottom linear path of the pallets with a reversely driven chain, a pallet transfer unit for lowering a pallet from a top path to a bottom path, and a pallet transfer unit for raising a pallet from a bottom path to a top path. At the top frame along the linear path are supported a plurality of work stations at each given space. Each work station equips a machinery for performing a work function on a workpiece carried by the pallet. Reffering to the prior art shown in FIG. 8, this pallet conveyor 1 includes an elongated frame 2 which constitutes a top linear path 4 of travel of pallets 8 with a continuously endless chain 3 and also provides tracks for rollers 9 of the pallet 8 along the run of the chain 3. At the bottom of the pallet 8 are mounted two idler sprockets 30 which can be easily driven by the chain 3 wherein the sprockets 30 are designed to be locked and attached to the chain 3 or to be unlocked and rotated themselves at their position by the operation of a clutch device 31. When the sprockets 30 rotate by themselves, the pallet 8 stops at its position. On the contrary, when the sprockets 30 are locked not to rotate by themselves, the sprockets 30 and hence the pallet 8 are attached to the chain 3 and are moved with the driven chain 3.
In the above prior art, each pallet 8 of the conveyor 1 needs to be equipped with a clutch device 31 which enables the sprockets 30 to be locked and attached to the chain 3 in order to move the sprockets 30 and hence the pallet 8 with the driven chain 31, and enables the sprockets 30 to rotate at their position in order to locate the pallet 8 at each work station. The clutch device 31 and sprockets 30 cause the pallet 8 very complicated. Besides, a plurality of elongated frames 2 are generally connected one after another in the line to increase the work stations for performing a plurality work functions. In the elongated conveyor 1, the sprocket 30 near the forward edge of the pallet 8 released from the chain 3 sometimes can not engage with a endless chain (not shown) in an adjacent frame and a tooth of the sprocket 30 can get on a cross pin which connects link plate structures of the chain 3. As under this condition, the pallet 8 moves furthermore to next station by means of the engagement between the sprocket 30 near the rear edge of the pallet 8 and the chain 3, so the pallet 8 is carried while its forward edge is lifted up to some extent. This causes a workpiece (not shown) carried by the pallet 8 to be misaligned and to fall down from the pallet 8. Besides, it causes the tooth of sprocket 30 to be broken so that the conveyor 1 gets never to move pallets 8 to workstations. Consequently the machines at the workstations can not continue performing work functions. Furthermore, in the conveyor the sprockets 30 are biased by a spring 32 to release a overload which might be caused to the sprockets 30 being driven by the chain 3 when the pallet 8 is about to be positioned. Therefore, the biased spring 32 must be changed to a proper spring preventing from releasing a load which is caused to the sprocket 30 when the pallet 8 carries a heavier workpiece. This job for chainging the springs can not easily be done without disassembling a pallet 8.